A Researcher Is Interested in Determining the Kinetics of Synthesis

Multiple Choice

A researcher is interested in determining the kinetics of synthesis and secretion of a protein that is known to be produced by kidney cells.The researcher modifies the gene by inserting a sequence encoding a region of a protein that can be visualized in the electron microscope.The marker is inserted just after the codon for the initiating methionine, within a region of hydrophobic amino acid residues.To determine the kinetics, the researcher will track the green-labeled proteins as they are synthesized in the RER, pass through the Golgi apparatus, and arrive at the cell surface in secretory vesicles.To the researcher's surprise, the green-labeled protein accumulates in the cytoplasm of the kidney cells and none appears in the RER, Golgi apparatus, or secretory vesicles.When the researcher repeats the experiment, but with the genetic marker inserted at the 3′ end of the gene just before the stop codon, the experiment proceeds as expected.These results indicate that, unintentionally, the researcher has confirmed that

A) the green genetic marker directs proteins to the cytoplasm.
B) secreted proteins accumulate in the cytoplasm before entering secretory vesicles.
C) the signal peptide sequence directing this protein to the RER is found in the hydrophobic region at its N terminus region.
D) secreted proteins do not have to travel through the Golgi apparatus.
E) a posttranslational modification directs the protein to the RER.